That "one tip" may already have come in perhaps... but a second good tip wouldn't hurt, either, and LE may be in no big hurry, espec if they feel the girls were targeted (as do I).
LE may be just shoring things up, their eye on assuring a conviction rather than arresting prematurely if they still have evidence being tested ("we are just now beginning") or if they are waiting for some personal alliances to break down in order to get someone (or a group of people?) to break down and talk.
Something stunning happened to bring about that 4/22 PC.
Rather than feel dismayed to see NBG's face (the sketch) I see it as a major breakthrough. Someone LIED to LE. They KNOW that now.
I think the car request is, as someone else suggested here, a means to ascertain which specific males were in the vicinity of the suspect vehicle that day at that time... to help in narrowing things down from a wider group of suspects certain evidentiary results may have handed them.
I think the vehicle carried BG and one other person. Maybe that person hung out while BG was with the girls. It wasn't supposed to end this way, IMO. Now this "other person" (NBG) is afraid to OUT BG. The NBG sketch may be of this other person (who was seen by someone in the vicinity of the car that day) ... this person may have been indirectly "responsible for the murders" ... yet is not himself BG.
LE may have lied when they said NBG sketch is the person on bridge with girls, to prompt BG to act (in order to protect NBG, whom BG knows was not on bridge). Maybe they are not really the same person, it's instead a ruse LE is using to force BG to talk or act?
Maybe BG was there to intercept the girls for some reason and things got way out of hand. Maybe girls knew sonething. Or maybe something had happened between one of the girls and "the other person" (NBG) such as (an example only!) an earlier SA or physical contact, something along those lines... so BG was trying to "fix" it but was too forceful, girls fought back, injury occurred, BG then felt he had to finish things off, and did so.
BG is not only a murderer but a coward who is letting NBG stand in as the "face" of the killer when NBG is not really the killer at all. I think LE is trying to work on BG's protective instinct toward NBG by using NBG as a fall guy but so far the cowardly BG is still not talking.
MOOOOOOOOOOOOOOOO!!!!!